The present invention relates to an oscilloscope triggering control circuit and particularly to such a circuit wherein triggering is selectable among a number of triggering events.
In a device such as a oscilloscope, a display sweep is initiated by a trigger signal presented to a sweep generator. Following the display sweep, a recovery period, known as the holdoff period, is required to allow time for the electron beam to return to the left side of the display screen, i.e., to retrace, and to allow time for the sweep generator to stabilize and prepare for the next display sweep.
The trigger signal is generated using an input signal from a predetermined source, and is usually derived from the signal to be displayed by the oscilloscope. The trigger signal comprises a stream of potential trigger points, each a possible candidate for initiating a trigger.
The holdoff on many oscilloscopes has the effect of selecting or locking the specific event displayed from a repetitive input signal. Thus, since the sweep cannot be triggered by a triggering event until the conclusion of the holdoff period, the holdoff period determines the next effective triggering event. When sweep holdoff is utilized in this manner to determine the particular portion of a repetitive signal for viewing, selection of the desired triggering event is frequently obtained by painstaking readjustment of the trigger level control or similar control until the event of interest just happens to trigger the oscilloscope. Once the event of interest is displayed, the oscilloscope will remain locked in correct repetitive operation.